Keywords

Introduction

Cardiac surgical patients use 10-20% of the nation's blood products [1]. Recent work [2] suggests a lower acceptable haematocrit for cardiac surgical patients during the perioperative period. This, and a change in our unit's policy to increase the availability of platelets and clotting factors (`crash packs') for these patients, prompted us to conduct this audit in order to determine whether our therapy was appropriately targeted.

Method

During a 3-month period we issued forms to the attending anaesthetist for all cardiac surgical procedures requesting information regarding demographics, preoperative drug history and baseline haematology. Intraoperative use of and indications for packed cells, fresh frozen plasma and platelets were noted. Postoperatively the attending nurse recorded the haematocrit, drain losses, and the use of and indications for red cells and clotting factors. Coagulation studies, and haemoglobin on CICU discharge and hospital discharge were also documented.

Results

Out of a possible 245, 183 forms were returned. Before bypass, 5.6% of patients were given blood, all of whom received 1 unit (mean haematocrit of 24.6%); the remainder had a mean haematocrit of 34.5%. Blood was received by 8.5, 0.6 and 0.6% (1, 2 and 3 units, respectively) on pump, with mean trigger haematocrits of 17.9, 18 and 19%, respectively. Postpump, 1.8% received blood, 1 unit each (mean haematocrit of 20.3%) versus 98.2% whose mean haematocrit was 22.7%. Overall, intraoperatively 83.6% received no blood, and 14.7% received only 1 unit of packed red cells (PRC). On CICU admission the mean haematocrit was 27% (no blood given), 24% (1 unit PRC), 21% (2 units PRC) and 19% (3 units PRC). The mean haematocrit on discharge from CICU was 27.8% where no blood was given, compared with 26.7%. Only one patient left hospital with a haemoglobin of below 8 g/dl. That patient had received no PRC. Of the 12% of patients who received 2 units PRC, 55% left hospital with a haemoglobin greater than 10 g/dl (12 out of 22); of the 4% of patients who received 5 units PRC, 57% left hospital with a haemoglobin greater than 10 g/dl (four out of seven). Of the 12% of patients who received only 1 unit PRC, 31% left hospital with a haemoglobin greater than 10 g/dl (four out of 13). Overall, 40% of patients received no blood during their admission, whereas 11% received only 1 unit of PRC. Patients weighing less than 60 kg had significantly greater PRC use, with 100% of this group requiring blood (mean 3 units/patient), compared with 53% of those who were over 60 kg in weight (mean 1.4 units/patient).

Fifteen per cent of patients received a `crash pack' in CICU. Only 68% of these had formal coagulation studies done. Of these only 20% had abnormal screens, defined as prothrombin time and partial thromboplastin time greater than 3 and 5s over control, respectively. Of those who received a crash pack, only 48% had a full blood count done first. Of these only 20% had platelet counts below 100×10/l. Only one patient of the six who had fibrinogen measured had levels below 1; five had `crash packs'. The mean total drainage was 1725 ml where a crash pack was given, compared with 797 ml where no clotting factors were given. The mean drainage in the 4.4% of patients done `off-pump' was 1120 ml, compared with 901 ml in the 95.6% whose procedures were performed on cardiopulmonary bypass (CPB). The mean CICU admission haematocrit was 32% (off-pump) versus 26% (post-CPB). Those done `off-pump' were given a mean of 2 units PRC versus 1.7 units PRC in those done on CPB. Of cases done off-pump, 33% had a crash pack. All of the 4.6% who were re-explored had crash packs.

Preoperative medication made no difference to mediastinal drainage or to crash pack use. The drain losses and crash pack use in smokers was no different from that in nonsmokers.

Conclusion

The present results suggest that our use of red cells could be targeted at lower haematocrits both intraoperatively and in CICU. There is a subgroup of patients who are given relatively small transfusions and are discharged with high haemoglobin concentrations. It would be prudent to evaluate means to avoid this, and this may particularly benefit those weighing below 60 kg. The drain losses and transfusion requirements in those patients undergoing coronary artery bypass grafting `off-pump' were significantly higher than expected, although this sample was small and may reflect a `learning curve'. Those patients receiving clotting factors and platelets had significantly higher mediastinal drainage than those who did not. Only a small percentage of postoperative coagulation studies/platelet counts were abnormal. From our current data it is difficult to assess the contribution to haemostasis of the blood products given. A more accessible/rapid assessment of the coagulation system and platelet numbers and function may be helpful in directing our use of clotting factors and platelet concentrate.